Google Sites, driven primarily by video viewing at YouTube.com, ranked as the top online video content property in December with 153 million unique viewers, followed by Facebook.com with 58.8 million, VEVO with 51.6 million, NDN with 49.9 million and Yahoo! Sites with 47.5 million.

Nearly 38.7 billion video content views occurred during the month, with Google Sites generating the highest number at 13.2 billion, followed by AOL, Inc. with 692 million.

Once again, Google Sites had the highest average engagement among the top ten properties.

Americans viewed 11.3 billion video ads in December, with Google Sites ranking first with nearly 2 billion advertisement views. BrightRoll Video Network came in second with 1.8 billion, followed by Liverail.com with 1.8 billion, Adap.tv with 1.5 billion and Hulu with 1.5 billion.

Video ads reached 53 percent of the total U.S. population an average of 70 times during the month.

Hulu delivered the highest frequency of video ads to its viewers with an average of 65, while Google Sites delivered an average of 20 ads per viewer.

The December 2012 YouTube partner data revealed that video music channel VEVO maintained the top position in the ranking with 50.5 million viewers.

Fullscreen climbed into the #2 position for the first time with 31.1 million viewers, followed by Maker Studios Inc. with 30 million, Warner Music with 26 million and Machinima with 26 million.

Among the top 10 YouTube partners, Machinima demonstrated the highest engagement (68 minutes per viewer) followed by Maker Studios (44 minutes per viewer). VEVO streamed the greatest number of videos (565 million), followed by Machinima (503 million).

Other findings from December 2012 study include:

84.9 percent of the U.S. Internet audience viewed online video.

The duration of the average online content video was 5.4 minutes, while the average online video ad was 0.4 minutes.

Video ads accounted for 22.6 percent of all videos viewed and 1.9 percent of all minutes spent viewing video online.